Prime Minister Jacinda Ardern is calling out National for "reneging" on its word and says it has become clear to her that the party cannot be taken on its word.

Her comments come as Justice Minister Andrew Little continues to attempt to get National across the line to support a new anti-terrorism bill.

Tensions between National and the Government have been simmering since the bill was introduced last week.

Little this morning said the Government had been "dicked around" by National over the issue, to which Bridges said that the Justice Minister's negotiation style was "belligerent".

The bill – which aims to give police more power to deal with those who have engaged in terrorism-related activities overseas if they return to New Zealand – was meant to go before Parliament for its first reading today.

But it appears as if the bill's first reading has been pushed back.

It is now unclear when it will go before the House but it is unlikely to do so soon, if the Government can't get the numbers to get it to pass.

The Greens have said it would not support the first reading of the bill as it stands, but have left the door open to supporting the bill if its demands are met.

Ardern today took aim at National, putting the blame for the delay directly in National Leader Simon Bridges' lap.

"They did give the Minister written confirmation that they would support the returning foreign fighters' legislation, they have then reneged on their word."

This morning, Little released an email – sent on Tuesday last week – from National which confirmed that it would be supporting the bill in its first reading.

The email did not mention anything about any changes National would like to see to the legislation.

National had promised to support the bill, but threatened to pull that support if Little refused to meet Bridges to discuss its demands.

They met yesterday, but National has not yet confirmed it will support the first reading.

Ardern said today: "I think if you have written confirmation that there will be support at first reading for a bill, you take the opposition at their word."

"Obviously," she said, "that hasn't proven to be the case here, which is very disappointing."

This morning, National pushed back on the suggestion it had been unco-operative over the vote.

"We have been very clear from day one what we wanted – none of our amendments have changed, they are still all the same amendments on the table and there has been no change at all," National's justice spokesman Mark Mitchell said.

Speaking to media this afternoon, Greens Foreign Affairs spokeswoman MP Golriz Ghahraman said the party was open to supporting the bill, if certain changes are met.

"We have always been really open to speaking with the Minister and we have been speaking with [Little] over the last week."

She said the Greens were open to making the law "the kind of law it needs to be to keep New Zealand safe".

The Greens want the definition of terror, as defined by the bill, to be a New Zealand definition and not that of an overseas jurisdiction.